Step 1: Roast the Garlic. Preheat your oven to 400°F (200°C). Place the halved garlic head on a sheet of aluminum foil, drizzle with a tablespoon of olive oil, and wrap it up tightly. Roast in the oven for about 30-35 minutes, until the cloves are soft and caramelized. Let it cool slightly, then squeeze the roasted garlic into a bowl, discarding the skins.
Step 2: Prepare the Dough. In a mixing bowl, combine the warm water and the active dry yeast. Let it sit for about 5 minutes until it becomes frothy. Add the roasted garlic, the remaining olive oil (reserving a tablespoon for drizzling later), and the fine grain sea salt. Stir to combine.
Step 3: Add the Flour. Gradually add the white flour to the yeast mixture, stirring with a wooden spoon or spatula until a shaggy dough forms. Transfer the dough to a floured surface and knead for about 5-7 minutes until smooth and elastic.
Step 4: First Rise. Place the kneaded dough in a lightly oiled bowl, covering it with plastic wrap or a damp towel. Let it rise in a warm spot for about 1 to 1.5 hours, or until it has doubled in size.
Step 5: Shape the Focaccia. Once the dough has risen, transfer it to a greased baking sheet. Gently stretch and press the dough out to fit the dimensions of the pan. Use your fingertips to create dimples across the surface.
Step 6: Second Rise. Cover the dough again and let it rise for another 30-45 minutes. Preheat your oven to 425°F (220°C).
Step 7: Add Toppings. Once the dough has risen, drizzle the reserved tablespoon of olive oil over the top and sprinkle with coarsely chopped rosemary and flaky sea salt.
Step 8: Bake. Place the baking sheet in the preheated oven and bake for 25-30 minutes, or until the focaccia is golden brown and sounds hollow when tapped on the bottom.
Step 9: Cool and Serve. Once baked, remove the focaccia from the oven and allow it to cool for a few minutes on a wire rack. Slice it into squares or wedges and serve warm.